Tool for dimpling



June3, 1947 o. w. ALBERT ETAL 2,421,732

f Tool. FOR DlMPLING f Filed Nov. 19, 1943v Ear l y n s Q O,

4 v Orrin W. Albert David Webster By Z .zx

` Agent Patented June 3, 1947 Orrin W; Albert and David A. Welistenurhank,

Calif.,A assignors; to Lockheed'Aircraft Corporation, Burbank; forni'a Cal'fg a corporation oli Cali-A Application November 19, 1943, Serial No. 510,978

6 Claims. l,

This invention relates to forming tools. and methods, and relates more particularly to a means and method for forming dimples at, the rivetV and screw receivingY openings of sheets. plates, etc.

In the fabrication of airplane components it is common practice to dimple the rivet receiving openings. so that the rivets may be. ush set or countersunk.

of` the conventional dimpling. punches and dies, the sheets. are warped and deformed. The warping of the sheet material is the result of stretching and/or shrinking of the sheet along itsv edge portion where the openings are, dimpled. The stretching and/or shrinking is caused by straining ofthe. material beyond the limits of the dimples, and whereA there are one or more rows of closely spaced dimpled openings adjacent the edge of a. sheet the warpingis often substantial. The warping occursin a. direction parallel to the plane of the sheet, and usually also in. a plane perpendicular to the plane of the sheet. The last named. form of warping. may be. easily remedied, but the curvature or warpingA in the plane. of the sheet is practically impossiblev to correct. This, irremediable deformation. of the sheet. is. the major cause of` the misalignment of the dimpled openings with openings in the substructureand also results in poor mating of the skin sheets. and irregularities in the assembled sheets.

It is an important object of the present invention to provide a. rapid, effective and commercially practical method for dimplingopenings in sheets and plates, which method completely avoids warping. and deformation of the sheets andplates.

Another object of the-invention is to provide a. method: for dimpling Openings in sheets and the like,` which connes the shaping andv straining of the sheet materialto the dimples` themselves and prevents straining of thecontiguous areas of the sheets'. In accordance withV the methodof the invention, the material is. confined, and securelyv heldin an. annular area spaced around the open.-` ingA during: the dimpling operationy to preclude the. possibility of` straining the material beyond the. dimple, The only portion of thesheet that is shaped and. strained is that portion which. constitutesthe dimple.

Another and importan-tobject of the invention is tol provide a double action` dimpling punch opg erable in conjunction with a di'e'to form dimples at. or around. openings in a sheet Without straining the surrounding sheet material adjacent the dimple, thereby preventing warping and deformation of thesheet.

Another object of the invention is to provide a double action dimplin-g punch embodying a.

Wherel rows, of closely spaced, openings are located adjacent the edges of the aluminum alloy. sheetsl and are dimpled by means.

clanoprlgV or confining sleeve which contacts the therebypreventingu straining and deforming of` thesheet beyond the dimple..

Another object ofthe invention is to provide a double action. dimpling punch embodyinga simple yet'4 very eflective means, for rst` transmitting movement, andl pressure to2 the clamping sleeve; andsubsequently operable to transmit movement and pressure to thedimpling punch while maintainingn the clamping pressure on the sleeve.

A further objectof the invention is to provide dimpling dies and punchesof the character referredr` to'4 that are operable. to rapidly andv effectively form dimples, without cracking or warping the sheet. The punches and dies of the' invention may serve. to form one or more rows of closely spacedA dimples, in the edge portion of a sheet without warping or cracking the sheet.

A further object ofthe; invention is to provi-de a simple. andy com-paotly constructed double `acting dimpli'ng punch adapted to be usedy in conjunction With a conventional type die'and in-a conventional imrlcil` press embodying a dampingsleeve adalted'to clamp the sheet immediately surrounding. the punch with a. force proportional to the punching force,Y

A. still further obj'ectoi" the inventionis to provide, a simple unitary double acting dimpling punch embodying a clamping sleeve adapted to clamp. the. sheet. immediately surrounding the punch with a. high. force. without employing complicateclf and` bulky mechanical apparatus, linkages and the. like.

Other objects and features of the invention will be .readily understood from. the. following detailedA description of a. typical preferred form of the invention throughout` which reference. kwill be made to the accompanying drawings. in which:

Figure l.- isa plan view of a plate or sheet. having 3.multiplicity of openings. that. have been` dimpled by means of conventional; dies, illustrating. the; manner in which the. sheet is, deformed or warped by the dimpling operation;

Figure. 2 is. a View` similar to Figure l showing a. plate or. sheet in which the. dimples. havebeen formed-by the method and tool of the invention;

Figure 3 is a longitudinal detailed sectional View, of the, die and. punch of` the invention showing theV sheet in position on the die; y

Figure 4 is a View similar to Figure 3 showing the.` clamping sleeve. in engagementv with the sheet; and; y

Figureis a view simil-ar to` Figure 3. showing the. punch in.. its iinal cli-mpiof forming position. The: dimpling dies and punches of the, invention. are, adaptedtd dimple openings in, sheets and plates of diiierent materials and of different configurations. yIn the drawings we have shown a simple form of the invention employed to dimple rows of staggered openings in the edge portion of a sheet of aluminum alloy of the type employed in airplane skins, It is to be understood that the invention is not to be construed as limited or restricted to the specic form or application herein described, but is to be considered broadly as including any features or modifications that may fall within the scope of the claims.

In Figure 1 we have illustrated a strip S of sheet stock having two rows of openings I extending along one longitudinal edge. The openings I0 of the individual rows are relatively close together and the outer row is in close relation to the edge of the strip. Annular tapering recesses or dimples II are provided in the strip S around the openings IIJ. The dimples II have been formed by typical or conventional dimpling punches and dies. The conventional dimpling devices have strained the material in areas beyond the dimples. As a result of this, an edge portion of the sheet S has been stretched longitudinally. The longitudinal stretching of the edge portion of the sheet has given the sheet a Vpermanent'set or warp so that its longitudinal edge I2 is convexedly curved. The warping in the plane of the sheet S makes it difficult if not impossible to accurately mate the sheet with a companion sheet and displaces the openings II) to positions where they will not register with openings in the substructure or other parts.

Figure 2 illustrates a similar sheet A having openings I3 in the same relationship as the openingsv II. The openings I3 of the sheet A have been provided with dimples I4 in accordance with the method and by the tools of the invention. The sheet A remains in its original rectangular conguration without warping in its plane or the perpendicular plane. Accordingly, the sheet A may be mated with companion sheets and its openings I3 will register with openings in the substructure or other parts.

The dimpling tool of the invention may be said to comprise generally a die I5, a punch holder I6, a clamping sleeve I'I in the holder l5, a punch I8 in the sleeve I'I, and elastic means I9 for transmitting pressure and movement from the holder I6 to the sleeve I'I and punch I8. In the drawings we have shown the die I as being the lower unit of the set. In practice the tool may be inverted so that the die forms the upper element and the invention is not to be considered as limited to the relationship of the parts shown in the drawings.

The die I5 may be a simple, one-piece member. It may be a substantially conventional die element. As illustrated, the die I5 comprises a head or body portion, and a reduced shank 20. The body of the diel5 bears on the end of the die support 2| and the shank 2i! is received in an opening 22 in the support. A central lVertical opening 23 enters the die I5 from its upper end and is provided to receive a part of the punch I8. A tapered bore or recess 24 is formed in the mouth of the opening 23 to assist in shaping the dimples. The recess 24 is annular and has a downwardly and inwardly slopingy wall. The upper end of the die I5 presents a flat annular surface surrounding the depressionV or recess 24. It is preferred to provide a slight radiusor curvature 25 at the junction of the recess 24 with the end of the die tovfacili- 4 tate drawing of the material intro the die and to slightly increase the area of the material over which the strain is distributed.

The punch holder I6 may be a simple onepiece socket member. Thel holder I5 is arranged Vagainst the lower end of its carrier 26.and has a reduced shank 21 extending upwardly into an opening 28 in the carrier. A central vertical socket 29 enters the holder I5 from its lower end and serves to receive or house the sleeve I'I, the punch I8 and the means I9.

The ring or sleeve I'I is an elongate tubular element which slidably engages in the socket 29. The sleeve II has a plain cylindrical exterior and a flat horizontal lower end.. The lower end of the sleeve Il directly opposes the end face ofthe die I5 and is adapted to contact the sheet A to clamp it against the die. The internal diameter of the sleeve I'i' is substantially the same as the largest diameter of the die recess 24. The sleeve I'I extends a considerable distance into the socket 29 to be adequately guided thereby. The upper internal corner 3E) of the sleeve I1 is rounded off.

, The upper portion of the sleeve I7 is enlarged in internal diameter as at 3I to provide the sleeve with an upwardly facing internal shoulder spaced some distance below the upper end of the sleeve. i

The punch I8 is arranged within the sleeve VI'I for longitudinal movement with respect thereto. The punch I8 is an elongate member whose major portion is cylindrical to slidably engage in the opening of the sleeve I'I. An annular ange or head 32 is provided on the upper end of the punch I8 and slidably fits the enlarged upper portion 3l of the sleeve opening. The head 32 is engageable with the shoulder at the lower end of the enlarged portion 3I of the opening to limit the downward movement of punch. A tapered stein or pilot 33 of reduced diameter projects from the lower end of the punch I8. The shoulder 34 which occurs at the root of the pilot 33 is the dimple forming surface of the punch. The shoulder or surface 34 is annular and slopes downwardly and inwardly at substantially the same angle as the wall of the die recess 24.

The means I9for transmitting movement from the holder IB to the sleeve I'I and punch I8 comprises a body 35 of elastic, owable material arranged in the socket 29 above the sleeve and the punch. The material 35 is such that it Yliows under pressure and is resilientor elastic to return to its original shape and proportions upon being relieved of pressure. It is desirable to employ a material having good flow characteristics and which will not break down with extended use. Raw latex has good ow characteristics and is durable but has a poor recovery upon bein-g relieved of pressure. We have found that cured rubber of about 40 Shore hardness rating is well suited for useV in the tool. The body lof elastic material 35 is shaped to completely occupythe socket 29 above'the sleeve I'I and punch I8 and serves tornormally hold these parts in the` positions illustrated in Figure 3.

The method of the invention will be described in connection with the operation ofthe die and punch set described above. Thesheet A, previcusly provided with the openings I3, is arranged between the die I5 and the punch means. VVVIt is to be understood that the die and punch means may be employed in individual sets or in gangs. `I`n the latter case, the plurality of sets may be operable to simultaneously dimple theseveral openings !3. With the die and punch in'tleir original or idle positions, the sleeve II and the punch pilot 33 -are 1 spaced-.above the die eso" that; the;v4 sheets A.

may b`e= readily@arrarigedl imposition oni the The sheetis positioned' to flatlybear onthe upper end-:1 of the die: 1151 and tohave its: opening.. I3 alignedwith :the dieiopeninig,r 234.1 Wltemthe sheet laieentproperitilpositiuned;l themiechanisrm with whichthedieandftpunchmeansf'are associated is operated@ to: produce .relativenmovementr between the die and? punchwelementsf..

ltwill .bei assumed that the. punch uniteissimoved downwardly. with'=` respectato`l` thef die.` (5..;` When the punchfzmeans is.' in .itat idler;4 on original.. posi` tion, the elastic; `materia-lI 35i? holdszthez.r sleeves; ITl in"` an.. extended position :wheres its: active lower end: 1 issadjacent-ther plane .olccupiethbn; the?. lower extremityo-fmhe pizlot133n-` The initialiphaseiotithe downwardzmovement ol'thepunch holder.' I6 bringsA thezlower end. of the sleeve Il into: enga-gement; `with-.trie sheet A. This. engagement; limits the:A downward, travelA of the sleeve.;4 and :as: the holder:u t6 continues-1 to-- move downwardly; the material 35.- is; compressed. betweenv. the.A downward-ly moving upperl Wall l oil the a socket` 29land the upper. ends-of. therrelative-lyi.stationarysleeve I1-and..punchl`4 I-8.-

the materia-i735: transmits downward pressure from.: the.- holder'. IIeto the.; sleeve I'I'` andthe'l sleeve is tightly forced againstA theasheetzA;A An annular area or zone of the sheet A spaced around the opening I3 is conned or clamped betweenzthelend face of the sleeve I'I andthe end face of the die. I5.. Figure 4 of the drawings shows the sleeve". IT'in its work clamping position. The hold'er I'6 continues to Imove downwardly and:` the: compressive force exertedon the annular zone of the sheetis increased until the Zone is under` alhighcornpression.

The/,material 35 is compressed lduring ,theactuation ofthe clamping sleeveA |'I`,`.as above. described, and' is displaced from between the upper end. of thesl'eeve and the upperwall socketLZQ tow downwardly into the sleeve. Itis preferred..toeproportion the parts so. that.there is always a substantial body ofthe material35between the upper endloiltlresleeve:A I'I and the top wall .ofthe socket 29 even A.vviththe parts inthei-r ful-1y actuated positions. The material35displacedl or. compressedintothe. sleeve I'Ir forces the punch I3 downwardly relative to the sleeve which is held against further downward movement by reason of its engagement with the sheet A. Thus as the holder I6 continues its downward travel, the punch IB' is forcibly moved downwardly within the sleeve. During the first portion of this downward movement of the punch its pilot 33 passes downwardly through the opening I3 into the opening 23. During the final portion of downward travel of the punch I8 the dimpling surface 34 engages the sheet A around the opening I 3 and presses it downwardly against the wall 24 of the die I5 to form the dimple. This shaping or forming of the dimple occurs while a surrounding annular section of the sheet A is compressed between the sleeve I'I and the end or the die I5.

The confining or clamping, under pressure, of the annular zone of the sheet A around the dimple area prevents straining of the sheet beyond the dimple itself. In this connection it is to be noted that the compressive force on the annular zone of the sheet A surrounding the dimple is at its maximum when the dimple is formed. In actual practice, it has been found that the confining or compressing of the sheet between the annular dimple surrounding faces of the die I and sleeve I'I positively restricts all straining of the sheet 6.. to:` the L actual; dimple;` and'. no: part; of: the sheet" beyondtthefdimpleisstrainedzor stressedt. Accord# ingly; therlsheetcr isi not:deformediiorwarpedf any way even in instanceswhere; closelyf. spaced openings Yad'ja'c'em: ani edge off arr'. elongatefsheet ameadimpled.

ittemptsr have been made; to: accomplish.; al similar result byE ernlvl'oy-ing springs or. spring actuated clamping devices. Su'clrattemptshave notLbeenzsuccessfirl ibecausenfthr; springs' necessary to obtain.` the required pressure must Vbesexces.-l sively.-large:.in:.:4 relation .to athesize. of.: thenpunchi lllurthermore; a.. tool; employing a; spring f, isi. noty perfectly. adaptable: for dimplingsheetsvot dilery-fv ent thickness;A Inw'the: toolxof. thefpresentxinlverre tion'ithe use of? springsxis: completely avoided; and the hold; down pressurel isA always; proportional to the.. dimplformingA pressure irrespective of the sheet l thickness.'A andi; other 1 factors.

At the: completion ofxthe dimple formingzactiorr they holder. Idir-novias. upwardly, .withdrawing f.' the pilot :.335from the: opening I3! and .disengagingthe punch and the sleeve I'I from thesheet Ae freeing the sheet for removal. Upon such upward .movement ofrthe. holder: I6s,.the';elastic mateciat, returns toitsr original .configuration and:` restores theesleeveI I1 andlthe' I8'. ttheirnormal idle positional Thus: ,the die unitis automaticallyconditi-cmdl for the next operation..`

From `the above description fofroperation of the tool it .will be: seenthatthe `methnd :otrtheinvene tion for formingadimple: in a piece of` work.c'om-. prises generally the steps of confining or-clamps ing. the `work.Y aro-und the. area. `to beudi'mpled. and the .shaping or i formingqof the dimple` while tai-ning .the clamping pressure; around` thefarea to prevent` straining. and deforming. offthe;I work: be.- yond z thek l dimple.-

Havifngl. described:` only; a typical; fornnof.; the invention-wezdomot wish to bei limited:` tolfthe specic details.A herein setforth; but wislfr4 toere-v serve to ourselves any variations or modifications thatrmayappea-r to those skilled I,intheart or fall within the. scope.: of the-following claims.4

Weclaim:

1.. Atool for providinga recessinalsheetcom-f prising adie having a concave die surface and `a face surrounding the die surface, a holder; the die and holder being related for relative movement, a punch axially movable in the holder and having a convex surface opposing the die surface, a pressure sleeve around the punch axially movable with respect to the holder and punch and having a face opposing the die face for engaging the sheet, and a single element arranged between the holder and the sleeve and punch for transmitting movement from the holder to the sleeve so that the sheet is clamped between said faces, upon movement of the holder toward the die, and for transmitting movement from the holder to the punch during continued Imovement of the holder toward the die so Ithat the punch and die surfaces form the recess in the sheet.

2. A tool for providing a recess in a sheet comprising -a die having a concave die surface and a face surrounding the die surface and adapted to engage a surface of the sheet, a holder having a socket and movable toward the die, a movable sleeve in the socket projecting from the holder to have a face opposing the face of the die, a punch movable in the sleeve and having a convex surface opposing the die surface, and means in the socket operable to transmit movement to the sleeve, upon movement of the holder toward the die, to bring the face of the sleeve against the sheet so vpunch movable in the sleeve and having a convex surface opposing the die surface, and a body of elastic flowable material in the socket for transmitting movement from the holder to the sleeve to bring the face of the sleeve into engagement withV the sheet so that the sheet is clamped between said faces during the initial portion of movement of the holderand adapted to flow into the sleeve during continuing movement of the holder lto move the punch against the sheet to form the recess while the sheet is cl-amped be tween said faces.

4. A dimpling tool for use with a die having a surface with a die recess therein, the tool comprising a holder movable toward the die and having a socket with an end Wall facing toward said die surface, la sleeve slidable in the socket and projecting from the holder to engage a sheet on the die, a punch movable in the sleeve and having a convex face opposing the recess of the die, and a body of elastic owable material engaged between said end wall of the socket and the inner end of the sleeve for transmitting movement from the holder to the sleeve, during initial movement of the holder toward the die, to bring the sleeve against the sheet so that the sheet is clamped between the surface of the die and the sleeve and adapted to flow into the sleeve upon continued movement of the holder to move the punch against the sheet to form the dimple.'

5. A dimpling tool for use with a die having a die surface and an abutment surface around the die surface, the tool comprising a holder movable toward the die, the holder having a socket presenting an end wall which faces toward the'die, a

-sleeve slidableY in the socket and projecting from the socket to have its outer end engageable with initial movement of the holder to transmit move.

ment to the sleeve so that the sheet is clamped between the outer end of the sleeve and the abutment surface of the die and operable during continuing movement of the holder to maintain the sleeve in clamping engagement with the sheet and to flow into the sleeve and move the punch against the sheet to form a dimple therein.

6. A dimpling tool for use with a die having an end surface adapted to engage a work piece comprising a holder, a sleeve movably carried by the holder and having a work engaging surface opposing said surface of the die, abody of ilowable material between the holder and sleeve for transmitting movement from the holder to the sleeve, and a dmpling elementv movable in the sleeve and contacted bysaid iiowable material to 4be actuated by pressuretransmitted from the holder through said lowable material when movement of the sleeve is prevented by engagement of the sleeve with the work piece.

ORRIN W. ALBERT. DAVID A. WEBSTER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Great Britain Aug. 14, 1939 

